Method of measuring signal strength in a wireless sensor system

ABSTRACT

A low cost, robust, wireless sensor that provides an extended period of operability without maintenance is described. The wireless sensors are configured to communicate with a base unit or repeater. When the sensor unit detects an anomalous ambient condition (e.g., smoke, fire, water, etc.) the sensor communicates with the base unit and provides data regarding the anomalous condition. The sensor unit receives instructions to change operating parameters and/or control external devices.

REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of application Ser. No.11/562,313, filed Nov. 21, 2006, titled “WIRELESS SENSOR UNIT,” now U.S.Pat. No. 7,411,494, which is a continuation of application Ser. No.10/856,231, filed May 27, 2004, titled “WIRELESS SENSOR UNIT,” now U.S.Pat. No. 7,142,107, the disclosure of which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless sensor unit system providingbi-directional communication between a sensor (e.g., smoke sensor, firesensor, temperature sensor, water, etc.) and a repeater or base unit ina building protection system.

2. Description of the Related Art

Maintaining and protecting a building or complex is difficult andcostly. Some conditions, such as fires, gas leaks, etc. are a danger tothe occupants and the structure. Other malfunctions, such as water leaksin roofs, plumbing, etc. are not necessarily dangerous for theoccupants, but can nevertheless cause considerable damage. In manycases, an adverse ambient condition such as water leakage, fire, etc. isnot detected in the early stages when the damage and/or danger isrelatively small. Sensors can be used to detect such adverse ambientconditions, but sensors present their own set of problems. For example,adding sensors, such as, for example, smoke detectors, water sensors,and the like in an existing structure can be prohibitively expensive dueto the cost of installing wiring between the remote sensors and acentralized monitoring device used to monitor the sensors. Adding wiringto provide power to the sensors further increases the cost. Moreover,with regard to fire sensors, most fire departments will not allowautomatic notification of the fire department based on the data from asmoke detector alone. Most fire departments require that a specifictemperature rate-of-rise be detected before an automatic fire alarmsystem can notify the fire department. Unfortunately, detecting fire bytemperature rate-of-rise generally means that the fire is not detecteduntil it is too late to prevent major damage.

SUMMARY

The present invention solves these and other problems by providing arelatively low cost, robust, wireless sensor system that provides anextended period of operability without maintenance. The system includesone or more intelligent sensor units and a base unit that cancommunicate with the sensor units. When one or more of the sensor unitsdetects an anomalous condition (e.g., smoke, fire, water, etc.) thesensor unit communicates with the base unit and provides data regardingthe anomalous condition. The base unit can contact a supervisor or otherresponsible person by a plurality of techniques, such as, telephone,pager, cellular telephone, Internet (and/or local area network), etc. Inone embodiment, one or more wireless repeaters are used between thesensor units and the base unit to extend the range of the system and toallow the base unit to communicate with a larger number of sensors.

In one embodiment, the sensor system includes a number of sensor unitslocated throughout a building that sense conditions and report anomalousresults back to a central reporting station. The sensor units measureconditions that might indicate a fire, water leak, etc. The sensor unitsreport the measured data to the base unit whenever the sensor unitdetermines that the measured data is sufficiently anomalous to bereported. The base unit can notify a responsible person such as, forexample a building manager, building owner, private security service,etc. In one embodiment, the sensor units do not send an alarm signal tothe central location. Rather, the sensors send quantitative measureddata (e.g., smoke density, temperature rate of rise, etc.) to thecentral reporting station.

In one embodiment, the sensor system includes a battery-operated sensorunit that detects a condition, such as, for example, smoke, temperature,humidity, moisture, water, water temperature, carbon monoxide, naturalgas, propane gas, other flammable gases, radon, poison gasses, etc. Thesensor unit is placed in a building, apartment, office, residence, etc.In order to conserve battery power, the sensor is normally placed in alow-power mode. In one embodiment, while in the low power mode, thesensor unit takes regular sensor readings and evaluates the readings todetermine if an anomalous condition exists. If an anomalous condition isdetected, then the sensor unit “wakes up” and begins communicating withthe base unit or with a repeater. At programmed intervals, the sensoralso “wakes up” and sends status information to the base unit (orrepeater) and then listens for commands for a period of time.

In one embodiment, the sensor unit is bi-directional and configured toreceive instructions from the central reporting station (or repeater).Thus, for example, the central reporting station can instruct the sensorto: perform additional measurements; go to a standby mode; wake up;report battery status; change wake-up interval; run self-diagnostics andreport results; etc. In one embodiment, the sensor unit also includes atamper switch. When tampering with the sensor is detected, the sensorreports such tampering to the base unit. In one embodiment, the sensorreports its general health and status to the central reporting stationon a regular basis (e.g., results of self-diagnostics, battery health,etc.).

In one embodiment, the sensor unit provides two wake-up modes, a firstwake-up mode for taking measurements (and reporting such measurements ifdeemed necessary), and a second wake-up mode for listening for commandsfrom the central reporting station. The two wake-up modes, orcombinations thereof, can occur at different intervals.

In one embodiment, the sensor units use spread-spectrum techniques tocommunicate with the base unit and/or the repeater units. In oneembodiment, the sensor units use frequency-hopping spread-spectrum. Inone embodiment, each sensor unit has an Identification code (ID) and thesensor units attaches its ID to outgoing communication packets. In oneembodiment, when receiving wireless data, each sensor unit ignores datathat is addressed to other sensor units.

The repeater unit is configured to relay communications traffic betweena number of sensor units and the base unit. The repeater units typicallyoperate in an environment with several other repeater units and thuseach repeater unit contains a database (e.g., a lookup table) of sensorIDs. During normal operation, the repeater only communicates withdesignated wireless sensor units whose IDs appears in the repeater'sdatabase. In one embodiment, the repeater is battery-operated andconserves power by maintaining an internal schedule of when itsdesignated sensors are expected to transmit and going to a low-powermode when none of its designated sensor units is scheduled to transmit.In one embodiment, the repeater uses spread-spectrum to communicate withthe base unit and the sensor units. In one embodiment, the repeater usesfrequency-hopping spread-spectrum to communicate with the base unit andthe sensor units. In one embodiment, each repeater unit has an ID andthe repeater unit attaches its ID to outgoing communication packets thatoriginate in the repeater unit. In one embodiment, each repeater unitignores data that is addressed to other repeater units or to sensorunits not serviced by the repeater.

In one embodiment, the repeater is configured to provide bi-directionalcommunication between one or more sensors and a base unit. In oneembodiment, the repeater is configured to receive instructions from thecentral reporting station (or repeater). Thus, for example, the centralreporting station can instruct the repeater to: send commands to one ormore sensors; go to standby mode; “wake up”; report battery status;change wake-up interval; run self-diagnostics and report results; etc.

The base unit is configured to receive measured sensor data from anumber of sensor units. In one embodiment, the sensor information isrelayed through the repeater units. The base unit also sends commands tothe repeater units and/or sensor units. In one embodiment, the base unitincludes a diskless PC that runs off of a CD-ROM, flash memory, DVD, orother read-only device, etc. When the base unit receives data from awireless sensor indicating that there may be an emergency condition(e.g., a fire or excess smoke, temperature, water, flammable gas, etc.)the base unit will attempt to notify a responsible party (e.g., abuilding manager) by several communication channels (e.g., telephone,Internet, pager, cell phone, etc.). In one embodiment, the base unitsends instructions to place the wireless sensor in an alert mode(inhibiting the wireless sensor's low-power mode). In one embodiment,the base unit sends instructions to activate one or more additionalsensors near the first sensor.

In one embodiment, the base unit maintains a database of the health,battery status, signal strength, and current operating status of all ofthe sensor units and repeater units in the wireless sensor system. Inone embodiment, the base unit automatically performs routine maintenanceby sending commands to each sensor to run a self-diagnostic and reportthe results. The bases unit collects such diagnostic results. In oneembodiment, the base unit sends instructions to each sensor telling thesensor how long to wait between “wakeup” intervals. In one embodiment,the base unit schedules different wakeup intervals to different sensorsbased on the sensor's health, battery health, location, etc. In oneembodiment, the base unit sends instructions to repeaters to routesensor information around a failed repeater.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sensor system that includes a plurality of sensor unitsthat communicate with a base unit through a number of repeater units.

FIG. 2 is a block diagram of a sensor unit.

FIG. 3 is a block diagram of a repeater unit.

FIG. 4 is a block diagram of the base unit.

FIG. 5 shows one embodiment a network communication packet used by thesensor units, repeater units, and the base unit.

FIG. 6 is a flowchart showing operation of a sensor unit that providesrelatively continuous monitoring.

FIG. 7 is a flowchart showing operation of a sensor unit that providesperiodic monitoring.

FIG. 8 shows how the sensor system can be used to detected water leaks.

DETAILED DESCRIPTION

FIG. 1 shows a sensor system 100 that includes a plurality of sensorunits 102-106 that communicate with a base unit 112 through a number ofrepeater units 110-111. The sensor units 102-106 are located throughouta building 101. Sensor units 102-104 communicate with the repeater 110.Sensor units 105-105 communicate with the repeater 111. The repeaters110-111 communicate with the base unit 112. The base unit 112communicates with a monitoring computer system 113 through a computernetwork connection such as, for example, Ethernet, wireless Ethernet,firewire port, Universal Serial Bus (USB) port, bluetooth, etc. Thecomputer system 113 contacts a building manager, maintenance service,alarm service, or other responsible personnel 120 using one or more ofseveral communication systems such as, for example, telephone 121, pager122, cellular telephone 123 (e.g., direct contact, voicemail, text,etc.), and/or through the Internet and/or local area network 124 (e.g.,through email, instant messaging, network communications, etc.). In oneembodiment, multiple base units 112 are provided to the monitoringcomputer 113. In one embodiment, the monitoring computer 113 is providedto more than one compute monitor, thus allowing more data to bedisplayed than can conveniently be displayed on a single monitor. In oneembodiment, the monitoring computer 113 is provided to multiple monitorslocated in different locations, thus allowing the data form themonitoring computer 113 to be displayed in multiple locations.

The sensor units 102-106 include sensors to measure conditions, such as,for example, smoke, temperature, moisture, water, water temperature,humidity, carbon monoxide, natural gas, propane gas, security alarms,intrusion alarms (e.g., open doors, broken windows, open windows, andthe like), other flammable gases, radon, poison gasses, etc. Differentsensor units can be configured with different sensors or withcombinations of sensors. Thus, for example, in one installation thesensor units 102 and 104 could be configured with smoke and/ortemperature sensors while the sensor unit 103 could be configured with ahumidity sensor.

The discussion that follows generally refers to the sensor unit 102 asan example of a sensor unit, with the understanding that the descriptionof the sensor unit 102 can be applied to many sensor units. Similarly,the discussion generally refers to the repeater 110 by way of example,and not limitation. It will also be understood by one of ordinary skillin the art that repeaters are useful for extending the range of thesensor units 102-106 but are not required in all embodiments. Thus, forexample in one embodiment, one or more of the sensor units 102-106 cancommunicate directly with the base unit 112 without going through arepeater. It will also be understood by one of ordinary skill in the artthat FIG. 1 shows only five sensor units (102-106) and two repeaterunits (110-111) for purposes of illustration and not by way oflimitation. An installation in a large apartment building or complexwould typically involve many sensor units and repeater units. Moreover,one of ordinary skill in the art will recognize that one repeater unitcan service relatively many sensor units. In one embodiment, the sensorunits 102 can communicate directly with the base unit 112 without goingthrough a repeater 111.

When the sensor unit 102 detects an anomalous condition (e.g., smoke,fire, water, etc.) the sensor unit communicates with the appropriaterepeater unit 110 and provides data regarding the anomalous condition.The repeater unit 110 forwards the data to the base unit 112, and thebase unit 112 forwards the information to the computer 113. The computer113 evaluates the data and takes appropriate action. If the computer 113determines that the condition is an emergency (e.g., fire, smoke, largequantities of water), then the computer 113 contacts the appropriatepersonnel 120. If the computer 113 determines that the situationwarrants reporting, but is not an emergency, then the computer 113 logsthe data for later reporting. In this way, the sensor system 100 canmonitor the conditions in and around the building 101.

In one embodiment, the sensor unit 102 has an internal power source(e.g., battery, solar cell, fuel cell, etc.). In order to conservepower, the sensor unit 102 is normally placed in a low-power mode. Inone embodiment, using sensors that require relatively little power,while in the low power mode the sensor unit 102 takes regular sensorreadings and evaluates the readings to determine if an anomalouscondition exists. In one embodiment, using sensors that requirerelatively more power, while in the low power mode the sensor unit 102takes and evaluates sensor readings at periodic intervals. If ananomalous condition is detected, then the sensor unit 102 “wakes up” andbegins communicating with the base unit 112 through the repeater 110. Atprogrammed intervals, the sensor unit 102 also “wakes up” and sendsstatus information (e.g., power levels, self diagnostic information,etc.) to the base unit (or repeater) and then listens for commands for aperiod of time. In one embodiment, the sensor unit 102 also includes atamper detector. When tampering with the sensor unit 102 is detected,the sensor unit 102 reports such tampering to the base unit 112.

In one embodiment, the sensor unit 102 provides bi-directionalcommunication and is configured to receive data and/or instructions fromthe base unit 112. Thus, for example, the base unit 112 can instruct thesensor unit 102 to perform additional measurements, to go to a standbymode, to wake up, to report battery status, to change wake-up interval,to run self-diagnostics and report results, etc. In one embodiment, thesensor unit 102 reports its general health and status on a regular basis(e.g., results of self-diagnostics, battery health, etc.).

In one embodiment, the sensor unit 102 provides two wake-up modes, afirst wake-up mode for taking measurements (and reporting suchmeasurements if deemed necessary), and a second wake-up mode forlistening for commands from the central reporting station. The twowake-up modes, or combinations thereof, can occur at differentintervals.

In one embodiment, the sensor unit 102 use spread-spectrum techniques tocommunicate with the repeater unit 110. In one embodiment, the sensorunit 102 use frequency-hopping spread-spectrum. In one embodiment, thesensor unit 102 has an address or identification (ID) code thatdistinguishes the sensor unit 102 from the other sensor units. Thesensor unit 102 attaches its ID to outgoing communication packets sothat transmissions from the sensor unit 102 can be identified by therepeater 110. The repeater 110 attaches the ID of the sensor unit 102 todata and/or instructions that are transmitted to the sensor unit 102. Inone embodiment, the sensor unit 102 ignores data and/or instructionsthat are addressed to other sensor units.

In one embodiment, the sensor unit 102 includes a reset function. In oneembodiment, the reset function is activated by the reset switch 208. Inone embodiment, the reset function is active for a prescribed intervalof time. During the reset interval, the transceiver 203 is in areceiving mode and can receive the identification code from an externalprogrammer. In one embodiment, the external programmer wirelesslytransmits a desired identification code. In one embodiment, theidentification code is programmed by an external programmer that isconnected to the sensor unit 102 through an electrical connector. In oneembodiment, the electrical connection to the sensor unit 102 is providedby sending modulated control signals (power line carrier signals)through a connector used to connect the power source 206. In oneembodiment, the external programmer provides power and control signals.In one embodiment, the external programmer also programs the type ofsensor(s) installed in the sensor unit. In one embodiment, theidentification code includes an area code (e.g., apartment number, zonenumber, floor number, etc.) and a unit number (e.g., unit 1, 2, 3,etc.).

In one embodiment, the sensor communicates with the repeater on the 900MHz band. This band provides good transmission through walls and otherobstacles normally found in and around a building structure. In oneembodiment, the sensor communicates with the repeater on bands aboveand/or below the 900 MHz band. In one embodiment, the sensor, repeater,and/or base unit listen to a radio frequency channel before transmittingon that channel or before beginning transmission. If the channel is inuse, (e.g., by another devise such as another repeater, a cordlesstelephone, etc.) then the sensor, repeater, and/or base unit changes toa different channel. In one embodiment, the sensor, repeater, and/orbase unit coordinate frequency hopping by listening to radio frequencychannels for interference and using an algorithm to select a nextchannel for transmission that avoids the interference. Thus, forexample, in one embodiment, if a sensor senses a dangerous condition andgoes into a continuous transmission mode, the sensor will test (e.g.,listen to) the channel before transmission to avoid channels that areblocked, in use, or jammed. In one embodiment, the sensor continues totransmit data until it receives an acknowledgement from the base unitthat the message has been received. In one embodiment, the sensortransmits data having a normal priority (e.g., status information) anddoes not look for an acknowledgement, and the sensor transmits datahaving elevated priority (e.g., excess smoke, temperature, etc.) untilan acknowledgement is received.

The repeater unit 110 is configured to relay communications trafficbetween the sensor 102 (and, similarly, the sensor units 103-104) andthe base unit 112. The repeater unit 110 typically operates in anenvironment with several other repeater units (such as the repeater unit111 in FIG. 1) and thus the repeater unit 110 contains a database (e.g.,a lookup table) of sensor unit IDs. In FIG. 1, the repeater 110 hasdatabase entries for the Ids of the sensors 102-104, and thus the sensor110 will only communicate with sensor units 102-104. In one embodiment,the repeater 110 has an internal power source (e.g., battery, solarcell, fuel cell, etc.) and conserves power by maintaining an internalschedule of when the sensor units 102-104 are expected to transmit. Inone embodiment, the repeater unit 110 goes to a low-power mode when noneof its designated sensor units is scheduled to transmit. In oneembodiment, the repeater 110 uses spread-spectrum techniques tocommunicate with the base unit 112 and with the sensor units 102-104. Inone embodiment, the repeater 110 uses frequency-hopping spread-spectrumto communicate with the base unit 112 and the sensor units 102-104. Inone embodiment, the repeater unit 110 has an address or identification(ID) code and the repeater unit 110 attaches its address to outgoingcommunication packets that originate in the repeater (that is, packetsthat are not being forwarded). In one embodiment, the repeater unit 110ignores data and/or instructions that are addressed to other repeaterunits or to sensor units not serviced by the repeater 110.

In one embodiment, the base unit 112 communicates with the sensor unit102 by transmitting a communication packet addressed to the sensor unit102. The repeaters 110 and 111 both receive the communication packetaddressed to the sensor unit 102. The repeater unit 111 ignores thecommunication packet addressed to the sensor unit 102. The repeater unit110 transmits the communication packet addressed to the sensor unit 102to the sensor unit 102. In one embodiment, the sensor unit 102, therepeater unit 110, and the base unit 112 communicate usingFrequency-Hopping Spread Spectrum (FHSS), also known as channel-hopping.

Frequency-hopping wireless systems offer the advantage of avoiding otherinterfering signals and avoiding collisions. Moreover, there areregulatory advantages given to systems that do not transmit continuouslyat one frequency. Channel-hopping transmitters change frequencies aftera period of continuous transmission, or when interference isencountered. These systems may have higher transmit power and relaxedlimitations on in-band spurs. FCC regulations limit transmission time onone channel to 400 milliseconds (averaged over 10-20 seconds dependingon channel bandwidth) before the transmitter must change frequency.There is a minimum frequency step when changing channels to resumetransmission. If there are 25 to 49 frequency channels, regulationsallow effective radiated power of 24 dBm, spurs must be −20 dBc, andharmonics must be −41.2 dBc. With 50 or more channels, regulations alloweffective radiated power to be up to 30 dBm.

In one embodiment, the sensor unit 102, the repeater unit 110, and thebase unit 112 communicate using FHSS wherein the frequency hopping ofthe sensor unit 102, the repeater unit 110, and the base unit 112 arenot synchronized such that at any given moment, the sensor unit 102 andthe repeater unit 110 are on different channels. In such a system, thebase unit 112 communicates with the sensor unit 102 using the hopfrequencies synchronized to the repeater unit 110 rather than the sensorunit 102. The repeater unit 110 then forwards the data to the sensorunit using hop frequencies synchronized to the sensor unit 102. Such asystem largely avoids collisions between the transmissions by the baseunit 112 and the repeater unit 110.

In one embodiment, the sensor units 102-106 all use FHSS and the sensorunits 102-106 are not synchronized. Thus, at any given moment, it isunlikely that any two or more of the sensor units 102-106 will transmiton the same frequency. In this manner, collisions are largely avoided.In one embodiment, collisions are not detected but are tolerated by thesystem 100. If a collisions does occur, data lost due to the collisionis effectively re-transmitted the next time the sensor units transmitsensor data. When the sensor units 102-106 and repeater units 110-111operate in asynchronous mode, then a second collision is highly unlikelybecause the units causing the collisions have hopped to differentchannels. In one embodiment, the sensor units 102-106, repeater units110-110, and the base unit 112 use the same hop rate. In one embodiment,the sensor units 102-106, repeater units 110-110, and the base unit 112use the same pseudo-random algorithm to control channel hopping, butwith different starting seeds. In one embodiment, the starting seed forthe hop algorithm is calculated from the ID of the sensor units 102-106,repeater units 110-110, or the base unit 112.

In an alternative embodiment, the base unit communicates with the sensorunit 102 by sending a communication packet addressed to the repeaterunit 110, where the packet sent to the repeater unit 110 includes theaddress of the sensor unit 102. The repeater unit 102 extracts theaddress of the sensor unit 102 from the packet and creates and transmitsa packet addressed to the sensor unit 102.

In one embodiment, the repeater unit 110 is configured to providebi-directional communication between its sensors and the base unit 112.In one embodiment, the repeater 110 is configured to receiveinstructions from the base unit 110. Thus, for example, the base unit112 can instruct the repeater to: send commands to one or more sensors;go to standby mode; “wake up”; report battery status; change wake-upinterval; run self-diagnostics and report results; etc.

The base unit 112 is configured to receive measured sensor data from anumber of sensor units either directly, or through the repeaters110-111. The base unit 112 also sends commands to the repeater units110-111 and/or to the sensor units 110-111. In one embodiment, the baseunit 112 communicates with a diskless computer 113 that runs off of aCD-ROM. When the base unit 112 receives data from a sensor unit 102-111indicating that there may be an emergency condition (e.g., a fire orexcess smoke, temperature, water, etc.) the computer 113 will attempt tonotify the responsible party 120.

In one embodiment, the computer 112 maintains a database of the health,power status (e.g., battery charge), and current operating status of allof the sensor units 102-106 and the repeater units 110-111. In oneembodiment, the computer 113 automatically performs routine maintenanceby sending commands to each sensor unit 102-106 to run a self-diagnosticand report the results. The computer 113 collects and logs suchdiagnostic results. In one embodiment, the computer 113 sendsinstructions to each sensor unit 102-106 telling the sensor how long towait between “wakeup” intervals. In one embodiment, the computer 113schedules different wakeup intervals to different sensor unit 102-106based on the sensor unit's health, power status, location, etc. In oneembodiment, the computer 113 schedules different wakeup intervals todifferent sensor unit 102-106 based on the type of data and urgency ofthe data collected by the sensor unit (e.g., sensor units that havesmoke and/or temperature sensors produce data that should be checkedrelatively more often than sensor units that have humidity or moisturesensors). In one embodiment, the base unit sends instructions torepeaters to route sensor information around a failed repeater.

In one embodiment, the computer 113 produces a display that tellsmaintenance personnel which sensor units 102-106 need repair ormaintenance. In one embodiment, the computer 113 maintains a listshowing the status and/or location of each sensor according to the ID ofeach sensor.

In one embodiment, the sensor units 102-106 and/or the repeater units110-111 measure the signal strength of the wireless signals received(e.g., the sensor unit 102 measures the signal strength of the signalsreceived from the repeater unit 110, the repeater unit 110 measures thesignal strength received from the sensor unit 102 and/or the base unit112). The sensor units 102-106 and/or the repeater units 110-111 reportsuch signal strength measurement back to the computer 113. The computer113 evaluates the signal strength measurements to ascertain the healthand robustness of the sensor system 100. In one embodiment, the computer113 uses the signal strength information to re-route wirelesscommunications traffic in the sensor system 100. Thus, for example, ifthe repeater unit 110 goes offline or is having difficulty communicatingwith the sensor unit 102, the computer 113 can send instructions to therepeater unit 111 to add the ID of the sensor unit 102 to the databaseof the repeater unit 111 (and similarly, send instructions to therepeater unit 110 to remove the ID of the sensor unit 102), therebyrouting the traffic for the sensor unit 102 through the router unit 111instead of the router unit 110.

FIG. 2 is a block diagram of the sensor unit 102. In the sensor unit102, one or more sensors 201 and a transceiver 203 are provided to acontroller 202. The controller 202 typically provides power, data, andcontrol information to the sensor(s) 201 and the transceiver 202. Apower source 206 is provided to the controller 202. An optional tampersensor 205 is also provided to the controller 202. A reset device (e.g.,a switch) 208 is proved to the controller 202. In one embodiment, anoptional audio output device 209 is provided. In one embodiment, thesensor 201 is configured as a plug-in module that can be replacedrelatively easily.

In one embodiment, the transceiver 203 is based on a TRF 6901transceiver chip from Texas Instruments, Inc. In one embodiment, thecontroller 202 is a conventional programmable microcontroller. In oneembodiment, the controller 202 is based on a Field Programmable GateArray (FPGA), such as, for example, provided by Xilinx Corp. In oneembodiment, the sensor 201 includes an optoelectric smoke sensor with asmoke chamber. In one embodiment, the sensor 201 includes a thermistor.In one embodiment, the sensor 201 includes a humidity sensor. In oneembodiment, the sensor 201 includes a sensor, such as, for example, awater level sensor, a water temperature sensor, a carbon monoxidesensor, a moisture sensor, a water flow sensor, natural gas sensor,propane sensor, etc.

The controller 202 receives sensor data from the sensor(s) 201. Somesensors 201 produce digital data. However, for many types of sensors201, the sensor data is analog data. Analog sensor data is converted todigital format by the controller 202. In one embodiment, the controllerevaluates the data received from the sensor(s) 201 and determineswhether the data is to be transmitted to the base unit 112. The sensorunit 102 generally conserves power by not transmitting data that fallswithin a normal range. In one embodiment, the controller 202 evaluatesthe sensor data by comparing the data value to a threshold value (e.g.,a high threshold, a low threshold, or a high-low threshold). If the datais outside the threshold (e.g., above a high threshold, below a lowthreshold, outside an inner range threshold, or inside an outer rangethreshold), then the data is deemed to be anomalous and is transmittedto the base unit 112. In one embodiment, the data threshold isprogrammed into the controller 202. In one embodiment, the datathreshold is programmed by the base unit 112 by sending instructions tothe controller 202. In one embodiment, the controller 202 obtains sensordata and transmits the data when commanded by the computer 113.

In one embodiment, the tamper sensor 205 is configured as a switch thatdetects removal of or tampering with the sensor unit 102.

FIG. 3 is a block diagram of the repeater unit 110. In the repeater unit110, a first transceiver 302 and a second transceiver 305 are providedto a controller 303. The controller 303 typically provides power, data,and control information to the transceivers 302, 304. A power source 306is provided to the controller 303. An optional tamper sensor (not shown)is also provided to the controller 303.

When relaying sensor data to the base unit 112, the controller 303receives data from the first transceiver 303 and provides the data tothe second transceiver 304. When relaying instructions from the baseunit 112 to a sensor unit, the controller 303 receives data from thesecond transceiver 304 and provides the data to the first transceiver302. In one embodiment, the controller 303 conserves power bypowering-down the transceivers 302, 304 during periods when thecontroller 303 is not expecting data. The controller 303 also monitorsthe power source 306 and provides status information, such as, forexample, self-diagnostic information and/or information about the healthof the power source 306, to the base unit 112. In one embodiment, thecontroller 303 sends status information to the base unit 112 at regularintervals. In one embodiment, the controller 303 sends statusinformation to the base unit 112 when requested by the base unit 112. Inone embodiment, the controller 303 sends status information to the baseunit 112 when a fault condition (e.g., battery low) is detected.

In one embodiment, the controller 303 includes a table or list ofidentification codes for wireless sensor units 102. The repeater 303forwards packets received from, or sent to, sensor units 102 in thelist. In one embodiment, the repeater 110 receives entries for the listof sensor units from the computer 113. In one embodiment, the controller303 determines when a transmission is expected from the sensor units 102in the table of sensor units and places the repeater 110 (e.g., thetransceivers 302, 304) in a low-power mode when no transmissions areexpected from the transceivers on the list. In one embodiment, thecontroller 303 recalculates the times for low-power operation when acommand to change reporting interval is forwarded to one of the sensorunits 102 in the list (table) of sensor units or when a new sensor unitis added to the list (table) of sensor units.

FIG. 4 is a block diagram of the base unit 112. In the base unit 112, atransceiver 402 and a computer interface 404 are provided to acontroller 403. The controller 303 typically provides data and controlinformation to the transceivers 402 and to the interface. The interface402 is provided to a port on the monitoring computer 113. The interface402 can be a standard computer data interface, such as, for example,Ethernet, wireless Ethernet, firewire port, Universal Serial Bus (USB)port, bluetooth, etc.

FIG. 5 shows one embodiment a communication packet 500 used by thesensor units, repeater units, and the base unit. The packet 500 includesa preamble portion 501, an address (or ID) portion 502, a data payloadportion 503, and an integrity portion 504. In one embodiment, theintegrity portion 504 includes a checksum. In one embodiment, the sensorunits 102-106, the repeater units 110-111, and the base unit 112communicate using packets such as the packet 500. In one embodiment, thepackets 500 are transmitted using FHSS.

In one embodiment, the data packets that travel between the sensor unit102, the repeater unit 111, and the base unit 112 are encrypted. In oneembodiment, the data packets that travel between the sensor unit 102,the repeater unit 111, and the base unit 112 are encrypted and anauthentication code is provided in the data packet so that the sensorunit 102, the repeater unit, and/or the base unit 112 can verify theauthenticity of the packet.

In one embodiment the address portion 502 includes a first code and asecond code. In one embodiment, the repeater 111 only examines the firstcode to determine if the packet should be forwarded. Thus, for example,the first code can be interpreted as a building (or building complex)code and the second code interpreted as a subcode (e.g., an apartmentcode, area code, etc.). A repeater that uses the first code forforwarding thus forwards packets having a specified first code (e.g.,corresponding to the repeater's building or building complex). Thusalleviates the need to program a list of sensor units 102 into arepeater, since a group of sensors in a building will typically all havethe same first code but different second codes. A repeater soconfigured, only needs to know the first code to forward packets for anyrepeater in the building or building complex. This does, however, raisethe possibility that two repeaters in the same building could try toforward packets for the same sensor unit 102. In one embodiment, eachrepeater waits for a programmed delay period before forwarding a packet.Thus reducing the chance of packet collisions at the base unit (in thecase of sensor unit to base unit packets) and reducing the chance ofpacket collisions at the sensor unit (in the case of base unit to sensorunit packets). In one embodiment, a delay period is programmed into eachrepeater. In one embodiment, delay periods are pre-programmed onto therepeater units at the factory or during installation. In one embodiment,a delay period is programmed into each repeater by the base unit 112. Inone embodiment, a repeater randomly chooses a delay period. In oneembodiment, a repeater randomly chooses a delay period for eachforwarded packet. In one embodiment, the first code is at least 6digits. In one embodiment, the second code is at least 5 digits.

In one embodiment, the first code and the second code are programmedinto each sensor unit at the factory. In one embodiment, the first codeand the second code are programmed when the sensor unit is installed. Inone embodiment, the base unit 112 can re-program the first code and/orthe second code in a sensor unit.

In one embodiment, collisions are further avoided by configuring eachrepeater unit 111 to begin transmission on a different frequencychannel. Thus, if two repeaters attempt to begin transmission at thesame time, the repeaters will not interfere with each other because thetransmissions will begin on different channels (frequencies).

FIG. 6 is a flowchart showing one embodiment of the operation of thesensor unit 102 wherein relatively continuous monitoring is provided. InFIG. 6, a power up block 601 is followed by an initialization block 602.After initialization, the sensor unit 102 checks for a fault condition(e.g., activation of the tamper sensor, low battery, internal fault,etc.) in a block 603. A decision block 604 checks the fault status. If afault has occurred, then the process advances to a block 605 were thefault information is transmitted to the repeater 110 (after which, theprocess advances to a block 612); otherwise, the process advances to ablock 606. In the block 606, the sensor unit 102 takes a sensor readingfrom the sensor(s) 201. The sensor data is subsequently evaluated in ablock 607. If the sensor data is abnormal, then the process advances toa transmit block 609 where the sensor data is transmitted to therepeater 110 (after which, the process advances to a block 612);otherwise, the process advances to a timeout decision block 610. If thetimeout period has not elapsed, then the process returns to thefault-check block 603; otherwise, the process advances to a transmitstatus block 611 where normal status information is transmitted to therepeater 110. In one embodiment, the normal status informationtransmitted is analogous to a simple “ping” which indicates that thesensor unit 102 is functioning normally. After the block 611, theprocess proceeds to a block 612 where the sensor unit 102 momentarilylistens for instructions from the monitor computer 113. If aninstruction is received, then the sensor unit 102 performs theinstructions, otherwise, the process returns to the status check block603. In one embodiment, transceiver 203 is normally powered down. Thecontroller 202 powers up the transceiver 203 during execution of theblocks 605, 609, 611, and 612. The monitoring computer 113 can sendinstructions to the sensor unit 102 to change the parameters used toevaluate data used in block 607, the listen period used in block 612,etc.

Relatively continuous monitoring, such as shown in FIG. 6, isappropriate for sensor units that sense relatively high-priority data(e.g., smoke, fire, carbon monoxide, flammable gas, etc.). By contrast,periodic monitoring can be used for sensors that sense relatively lowerpriority data (e.g., humidity, moisture, water usage, etc.). FIG. 7 is aflowchart showing one embodiment of operation of the sensor unit 102wherein periodic monitoring is provided. In FIG. 7, a power up block 701is followed by an initialization block 702. After initialization, thesensor unit 102 enters a low-power sleep mode. If a fault occurs duringthe sleep mode (e.g., the tamper sensor is activated), then the processenters a wake-up block 704 followed by a transmit fault block 705. If nofault occurs during the sleep period, then when the specified sleepperiod has expired, the process enters a block 706 where the sensor unit102 takes a sensor reading from the sensor(s) 201. The sensor data issubsequently sent to the monitoring computer 113 in a report block 707.After reporting, the sensor unit 102 enters a listen block 708 where thesensor unit 102 listens for a relatively short period of time forinstructions from monitoring computer 708. If an instruction isreceived, then the sensor unit 102 performs the instructions, otherwise,the process returns to the sleep block 703. In one embodiment, thesensor 201 and transceiver 203 are normally powered down. The controller202 powers up the sensor 201 during execution of the block 706. Thecontroller 202 powers up the transceiver during execution of the blocks705, 707, and 708. The monitoring computer 113 can send instructions tothe sensor unit 102 to change the sleep period used in block 703, thelisten period used in block 708, etc.

In one embodiment, the sensor unit transmits sensor data until ahandshaking-type acknowledgement is received. Thus, rather than sleep ofno instructions or acknowledgements are received after transmission(e.g., after the decision block 613 or 709) the sensor unit 102retransmits its data and waits for an acknowledgement. The sensor unit102 continues to transmit data and wait for an acknowledgement until anacknowledgement is received. In one embodiment, the sensor unit acceptsan acknowledgement from a repeater unit 111 and it then becomes theresponsibility of the repeater unit 111 to make sure that the data isforwarded to the base unit 112. In one embodiment, the repeater unit 111does not generate the acknowledgement, but rather forwards anacknowledgement from the base unit 112 to the sensor unit 102. Thetwo-way communication ability of the sensor unit 102 provides thecapability for the base unit 112 to control the operation of the sensorunit 102 and also provides the capability for robust handshaking-typecommunication between the sensor unit 102 and the base unit 112.

Regardless of the normal operating mode of the sensor unit 102 (e.g.,using the Flowcharts of FIGS. 6, 7, or other modes) in one embodiment,the monitoring computer 113 can instruct the sensor unit 102 to operatein a relatively continuous mode where the sensor repeatedly takes sensorreadings and transmits the readings to the monitoring computer 113. Sucha mode can be used, for example, when the sensor unit 102 (or a nearbysensor unit) has detected a potentially dangerous condition (e.g.,smoke, rapid temperature rise, etc.).

FIG. 8 shows the sensor system used to detect water leaks. In oneembodiment, the sensor unit 102 includes a water level sensor and 803and/or a water temperature sensor 804. The water level sensor 803 and/orwater temperature sensor 804 are place, for example, in a trayunderneath a water heater 801 in order to detect leaks from the waterheater 801 and thereby prevent water damage from a leaking water heater.In one embodiment, a temperature sensor is also provide to measuretemperature near the water heater. The water level sensor can also beplaced under a sink, in a floor sump, etc. In one embodiment, theseverity of a leak is ascertained by the sensor unit 102 (or themonitoring computer 113) by measuring the rate of rise in the waterlevel. When placed near the hot water tank 801, the severity of a leakcan also be ascertained at least in part by measuring the temperature ofthe water. In one embodiment, a first water flow sensor is placed in aninput water line for the hot water tank 801 and a second water flowsensor is placed in an output water line for the hot water tank. Leaksin the tank can be detected by observing a difference between the waterflowing through the two sensors.

In one embodiment, a remote shutoff valve 810 is provided, so that themonitoring system 100 can shutoff the water supply to the water heaterwhen a leak is detected. In one embodiment, the shutoff valve iscontrolled by the sensor unit 102. In one embodiment, the sensor unit102 receives instructions from the base unit 112 to shut off the watersupply to the heater 801. In one embodiment, the responsible party 120sends instructions to the monitoring computer 113 instructing themonitoring computer 113 to send water shut off instructions to thesensor unit 102. Similarly, in one embodiment, the sensor unit 102controls a gas shutoff valve 811 to shut off the gas supply to the waterheater 801 and/or to a furnace (not shown) when dangerous conditions(such as, for example, gas leaks, carbon monoxide, etc.) are detected.In one embodiment, a gas detector 812 is provided to the sensor unit102. In one embodiment, the gas detector 812 measures carbon monoxide.In one embodiment, the gas detector 812 measures flammable gas, such as,for example, natural gas or propane.

In one embodiment, an optional temperature sensor 818 is provided tomeasure stack temperature. Using data from the temperature sensor 818,the sensor unit 102 reports conditions, such as, for example, excessstack temperature. Excess stack temperature is often indicative of poorheat transfer (and thus poor efficiency) in the water heater 818.

In one embodiment, an optional temperature sensor 819 is provided tomeasure temperature of water in the water heater 810. Using data fromthe temperature sensor 819, the sensor unit 102 reports conditions, suchas, for example, over-temperature or under-temperature of the water inthe water heater.

In one embodiment, an optional current probe 821 is provided to measureelectric current provided to a heating element 820 in an electric waterheater. Using data from the current probe 821, the sensor unit 102reports conditions, such as, for example, no current (indicating aburned-out heating element 820). An over-current condition oftenindicates that the heating element 820 is encrusted with mineraldeposits and needs to be replaced or cleaned. By measuring the currentprovided to the water heater, the monitoring system can measure theamount of energy provided to the water heater and thus the cost of hotwater, and the efficiency of the water heater.

In one embodiment, the sensor 803 includes a moisture sensor. Using datafrom the moisture sensor, the sensor unit 102 reports moistureconditions, such as, for example, excess moisture that would indicate awater leak, excess condensation, etc.

In one embodiment, the sensor unit 102 is provided to a moisture sensor(such as the sensor 803) located near an air conditioning unit. Usingdata from the moisture sensor, the sensor unit 102 reports moistureconditions, such as, for example, excess moisture that would indicate awater leak, excess condensation, etc.

In one embodiment, the sensor 201 includes a moisture sensor. Themoisture sensor can be place under a sink or a toilet (to detectplumbing leaks) or in an attic space (to detect roof leaks).

Excess humidity in a structure can cause sever problems such as rotting,growth of molds, mildew, and fungus, etc. (hereinafter referred togenerically as fungus). In one embodiment, the sensor 201 includes ahumidity sensor. The humidity sensor can be place under a sink, in anattic space, etc. to detect excess humidity (due to leaks, condensation,etc.). In one embodiment, the monitoring computer 113 compares humiditymeasurements taken from different sensor units in order to detect areasthat have excess humidity. Thus for example, the monitoring computer 113can compare the humidity readings from a first sensor unit 102 in afirst attic area, to a humidity reading from a second sensor unit 102 ina second area. For example, the monitoring computer can take humidityreadings from a number of attic areas to establish a baseline humidityreading and then compare the specific humidity readings from varioussensor units to determine if one or more of the units are measuringexcess humidity. The monitoring computer 113 would flag areas of excesshumidity for further investigation by maintenance personnel. In oneembodiment, the monitoring computer 113 maintains a history of humidityreadings for various sensor units and flags areas that show anunexpected increase in humidity for investigation by maintenancepersonnel.

In one embodiment, the monitoring system 100 detects conditionsfavorable for fungus (e.g., mold, mildew, fungus, etc.) growth by usinga first humidity sensor located in a first building area to producefirst humidity data and a second humidity sensor located in a secondbuilding area to produce second humidity data. The building areas canbe, for example, areas near a sink drain, plumbing fixture, plumbing,attic areas, outer walls, a bilge area in a boat, etc.

The monitoring station 113 collects humidity readings from the firsthumidity sensor and the second humidity sensor and indicates conditionsfavorable for fungus growth by comparing the first humidity data and thesecond humidity data. In one embodiment, the monitoring station 113establishes a baseline humidity by comparing humidity readings from aplurality of humidity sensors and indicates possible fungus growthconditions in the first building area when at least a portion of thefirst humidity data exceeds the baseline humidity by a specified amount.In one embodiment, the monitoring station 113 establishes a baselinehumidity by comparing humidity readings from a plurality of humiditysensors and indicates possible fungus growth conditions in the firstbuilding area when at least a portion of the first humidity data exceedsthe baseline humidity by a specified percentage.

In one embodiment, the monitoring station 113 establishes a baselinehumidity history by comparing humidity readings from a plurality ofhumidity sensors and indicates possible fungus growth conditions in thefirst building area when at least a portion of the first humidity dataexceeds the baseline humidity history by a specified amount over aspecified period of time. In one embodiment, the monitoring station 113establishes a baseline humidity history by comparing humidity readingsfrom a plurality of humidity sensors over a period of time and indicatespossible fungus growth conditions in the first building area when atleast a portion of the first humidity data exceeds the baseline humidityby a specified percentage of a specified period of time.

In one embodiment, the sensor unit 102 transmits humidity data when itdetermines that the humidity data fails a threshold test. In oneembodiment, the humidity threshold for the threshold test is provided tothe sensor unit 102 by the monitoring station 113. In one embodiment,the humidity threshold for the threshold test is computed by themonitoring station from a baseline humidity established in themonitoring station. In one embodiment, the baseline humidity is computedat least in part as an average of humidity readings from a number ofhumidity sensors. In one embodiment, the baseline humidity is computedat least in part as a time average of humidity readings from a number ofhumidity sensors. In one embodiment, the baseline humidity is computedat least in part as a time average of humidity readings from a humiditysensor. In one embodiment, the baseline humidity is computed at least inpart as the lesser of a maximum humidity reading an average of a numberof humidity readings.

In one embodiment, the sensor unit 102 reports humidity readings inresponse to a query by the monitoring station 113. In one embodiment,the sensor unit 102 reports humidity readings at regular intervals. Inone embodiment, a humidity interval is provided to the sensor unit 102by the monitoring station 113.

In one embodiment, the calculation of conditions for fungus growth iscomparing humidity readings from one or more humidity sensors to thebaseline (or reference) humidity. In one embodiment, the comparison isbased on comparing the humidity readings to a percentage (e.g.,typically a percentage greater than 100%) of the baseline value. In oneembodiment, the comparison is based on comparing the humidity readingsto a specified delta value above the reference humidity. In oneembodiment, the calculation of likelihood of conditions for fungusgrowth is based on a time history of humidity readings, such that thelonger the favorable conditions exist, the greater the likelihood offungus growth. In one embodiment, relatively high humidity readings overa period of time indicate a higher likelihood of fungus growth thanrelatively high humidity readings for short periods of time. In oneembodiment, a relatively sudden increase in humidity as compared to abaseline or reference humidity is reported by the monitoring station 113as a possibility of a water leak. If the relatively high humidityreading continues over time then the relatively high humidity isreported by the monitoring station 113 as possibly being a water leakand/or an area likely to have fungus growth or water damage.

Temperatures relatively more favorable to fungus growth increase thelikelihood of fungus growth. In one embodiment, temperature measurementsfrom the building areas are also used in the fungus grown-likelihoodcalculations. In one embodiment, a threshold value for likelihood offungus growth is computed at least in part as a function of temperature,such that temperatures relatively more favorable to fungus growth resultin a relatively lower threshold than temperatures relatively lessfavorable for fungus growth. In one embodiment, the calculation of alikelihood of fungus growth depends at least in part on temperature suchthat temperatures relatively more favorable to fungus growth indicate arelatively higher likelihood of fungus growth than temperaturesrelatively less favorable for fungus growth. Thus, in one embodiment, amaximum humidity and/or minimum threshold above a reference humidity isrelatively lower for temperature more favorable to fungus growth thanthe maximum humidity and/or minimum threshold above a reference humidityfor temperatures relatively less favorable to fungus growth.

In one embodiment, a water flow sensor is provided to the sensor unit102. The sensor unit 102 obtains water flow data from the water flowsensor and provides the water flow data to the monitoring computer 113.The monitoring computer 113 can then calculate water usage.Additionally, the monitoring computer can watch for water leaks, by, forexample, looking for water flow when there should be little or no flow.Thus, for example, if the monitoring computer detects water usagethroughout the night, the monitoring computer can raise an alertindicating that a possible water leak has occurred.

In one embodiment, the sensor 201 includes a water flow sensor isprovided to the sensor unit 102. The sensor unit 102 obtains water flowdata from the water flow sensor and provides the water flow data to themonitoring computer 113. The monitoring computer 113 can then calculatewater usage. Additionally, the monitoring computer can watch for waterleaks, by, for example, looking for water flow when there should belittle or no flow. Thus, for example, if the monitoring computer detectswater usage throughout the night, the monitoring computer can raise analert indicating that a possible water leak has occurred.

In one embodiment, the sensor 201 includes a fire-extinguisher tampersensor is provided to the sensor unit 102. The fire-extinguisher tampersensor reports tampering with or use of a fire-extinguisher. In oneembodiment the fire-extinguisher tamper sensor reports that the fireextinguisher has been removed from its mounting, that a fireextinguisher compartment has been opened, and/or that a safety lock onthe fire extinguisher has been removed.

It will be evident to those skilled in the art that the invention is notlimited to the details of the foregoing illustrated embodiments and thatthe present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributed thereof; furthermore,various omissions, substitutions and changes may be made withoutdeparting from the spirit of the inventions. For example, althoughspecific embodiments are described in terms of the 900 MHz frequencyband, one of ordinary skill in the art will recognize that frequencybands above and below 900 MHz can be used as well. The wireless systemcan be configured to operate on one or more frequency bands, such as,for example, the HF band, the VHF band, the UHF band, the Microwaveband, the Millimeter wave band, etc. One of ordinary skill in the artwill further recognize that techniques other than spread spectrum canalso be used and/or can be use instead spread spectrum. The modulationuses is not limited to any particular modulation method, such thatmodulation scheme used can be, for example, frequency modulation, phasemodulation, amplitude modulation, combinations thereof, etc. Theforegoing description of the embodiments is therefore to be consideredin all respects as illustrative and not restrictive, with the scope ofthe invention being delineated by the appended claims and theirequivalents.

1. A method of routing communication traffic in a wireless sensorsystem, comprising: measuring the signal strength of wireless signalsreceived by one or more wireless sensor units from a base unit and fromone or more wireless repeater units; measuring the signal strength ofwireless signals received by one or more wireless repeater units fromsaid base unit and from said one or more wireless sensor units;transmitting the signal strength measurements from said one or morewireless sensor units and said one or more wireless repeater units to acomputer; and selecting routing paths for communications based on anevaluation by said computer of said signal strength measurements.